This invention relates to overhead doors, and more particularly to cable drawn overhead doors having upper and lower sections arranged to be folded, one section upon the other during operation of the door between open and closed positions.
Sectioned overhead doors for use with aircraft hangers, warehouses and the like, all requiring particularly large openings, have been provided heretofore. However, such doors are characterized by structures which require that the door be supported against outward pivotal movement in open positions by heavy duty door rollers on the door and heavy duty guide tracks mounted to a building's strengthened door jambs. With the weight of these doors commonly being 1/2 to 1 ton or more, the supporting side structures and door guide assemblies require great strength, as the doors are arranged to bear their weight against the side tracks.
Particularly wherein structures involve unusually wide openings, such as aircraft hangers and the like, the door panels themselves must be made of strengthened materials in order to avoid sagging of the unsupported middle of the door in open position. Inexpensive light duty materials and mechanisms have heretofore been unsuitable for use in wide overhead doors for this reason, just as light duty door jamb structures are unsuitable to support strenghtened doors having great weights.
Exemplary of such prior art overhead doors are those disclosed in U.S. Pat. Nos. 1,709,872 and 1,588,663.